The primary goal of the project is to investigate the immunogenetic characteristics of alloantigen systems in the mouse. Particular emphasis is placed on the genetic analysis of the major histocompatibility gene complex and of genes adjacent to the MHC on Chromosome 17. Test cross offspring of selected hybrid parents are serologically tested and new H-2 recombinants are established as strains congenic with strain C57BL/10. The lines are used to further define the fine gene structure of the MHC and to use recombinant lines in the preparation of serological reagents with restricted specificity.